The k-general d-position problem for graphs

Abstract

A set of vertices of a graph is said to be in general position if no three vertices from the set lie on a common shortest path. Recently Klavžar, Rall and Yero generalized this notion by defining a set of vertices to be in general $d$-position if no three vertices from the set lie on a common shortest path of length at most $d$. We generalize this notion further by defining a set of vertices to be in $k$-general $d$-position if no $k$ vertices of the set lie on a common shortest path of length at most $d$. The $k$-general $d$-position number of a graph is the largest cardinality of a $k$-general $d$-position set. We provide upper and lower bounds on the $k$-general $d$-position number of graphs in terms of the $k$-general $d$-position number of certain kinds of subgraphs. We compute the $k$-general $d$-position number of finite paths and cycles. Along the way we establish that the maximally even subsets of cycles, which were introduced in Clough and Douthett’s work on music theory, provide the largest possible $k$-general $d$-position sets in $n$-cycles. We generalize Klavžar and Manuel’s notion of monotone-geodesic labeling to that of $k$-monotone-geodesic labeling in order to calculate the $k$-general $d$-position number of the infinite two-dimensional grid. We also prove a formula for the $k$-general $d$-position number of certain thin finite grids, providing a partial answer to a question asked by Klavžar, Rall and Yero.